This invention relates to a system for continuously monitoring and analyzing the power level and spectral quality of an RF or IF communication signal.
In communication systems, there is a problem of assuring the power level and spectral quality of the RF signal transmitted, or the IF output of a receiver. This problem is particularly acute in aerospace communications, where verification of the power level and spectral quality of a transmitter RF output, or a receiver IF output, is necessary in analyzing the command communications links to the spacecraft, and it is generally important in commercial communications, such as in TV or FM broadcasting.
It frequently happens that a transmitter malfunction will occur under particular environmental conditions, or will occur only momentarily. In either case there may be a failure in transmitting the proper communication. In the case of transmitting a command to a spacecraft, it is important to know that this failure has occurred in order to retransmit the command and/or to take corrective measures. However, to be able to take corrective measures, it is sometimes necessary to analyze the signal output of the transmitter at the time of the failure. In some cases retransmission of the command is sufficient, but in other case it is important to know what happened, and when, for complete analysis and corrective action. In the past it has been possible to determine only that there has been some failure in communications when the spacecraft fails to respond properly. By then it is not possible to analyze the transmitter output to determine the cause, unless the failure is a continuing one. For proper analysis, it is necessary that the failure be detected when it occurs, and that the transmitter output at the moment of failure be preserved for analysis. It is also useful to continuously monitor and analyze the power level and spectral quality of a receiver to detect the presence of an interfering signal, for example.